This proposal details the use of an in-situ cell optimised for use on the POLARIS beamline to study the structure-property relationships in the defect perovskite lithium insertion material Li0.18Sr0.66Ti0.5Nb0.5O3. Previous studies of lithium insertion into Li0.18Sr0.66Ti0.5Nb0.5O3 performed in-situ revealed a close correlation of the rate of change in the structure and the shape of the voltage profile. The current experiment is designed to establish the link between lithium occupancy, lithium position and observed properties as well as investigating how the structure changes as the lithium occupancy per vacant site goes beyond one.